I'm happy to announce we now have C# API for LDTP. Tested the API set with VB.NET and PowerShell.
Get latest LDTP binary from here
Credit: John Yingjun Li, who have done the most of work creating C# client, verifying with Linux LDTP, creating VB.NET test app.
API's tested against Cobra (Windows LDTP) and LDTP (Linux version, remotely though). Include Ldtp.dll and CookComputing.XmlRpcV2.dll into your project as dependency.
Check C# client and example source.